This application claims the benefit of Korean Application No. 2002-19824, filed on Apr. 11, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Filed of the Invention
The present invention relates to a multi band antenna built in a telecommunication terminal, and more particularly, to a planar inverted F antenna having a LC coupled feed line spaced-apart from a radiating patch by a predetermined distance to obtain multi frequency bands each having a wide frequency bandwidth.
2. Description of the Related Art
Recently, a mobile communication terminal is required to be compact, light, and multi-functional according to a recent demand. Electrical circuits and components built in the mobile communication terminal become smaller and multi-functional in order to satisfy the above requirement. Also, this requirement is applied to an antenna, which one of major components of the mobile communication terminal.
A conventional antenna used in the mobile communication terminal is a helical antenna and a planar inverted F antenna. The helical antenna is mounted on a top side of the mobile communication terminal together with a mono pole antenna. The helical antenna and the mono pole antenna have a quarter wavelength (xcex/4) and are disposed inside the mobile communication terminal to be extended to an outside of the mobile communication terminal together with the helical antenna.
Although the helical antenna has an advantage in obtaining a high gain in a frequency band, a characteristic of synthetic aperture radars (SAR), which is an industrial standard relating to an electromagnetic wave, becomes low due to a non-directional characteristic of the helical antenna. Moreover, because the helical antenna is built on an outside of the mobile communication terminal, the helical antenna is not suitable to a portable apparatus, and an outer appearance of the mobile communication terminal will not be neat. Furthermore, it is very difficult to design the mobile communication terminal to be compact since the monopole needs a space to be built inside the mobile communication terminal.
In an effort to overcome the above problems, the planar inverted F antenna has been proposed. FIG. 1 shows a structure of a conventional planar inverted F antenna (PIFA). The PIFA includes a radiating patch 2, a shorting pin 4, a coaxial line 5, a ground plane (plate) 9. The radiating patch 2 is electrically coupled to the coaxial line 5 and has an impedance match with the ground plane 9 by forming a short circuit. A length L of the radiating patch 2 and a height H of the PIFA are designed in accordance with a first width Wp of the shorting pin 4 and a second width of the radiating patch 2.
The PIFA reduces the amount of harmful electromagnetic waves generated toward a user because the electromagnetic waves generated by current induced in the radiating patch 2 and directed toward the ground plane 9 are re-induced to the radiating patch 2. Moreover, the SAR characteristic is improved by a directional increase of the radiation waves induced (directed) in a direction toward the radiating patch 2. Furthermore, the radiating patch 2, which is used as a rectangular micro strip antenna having a predetermined length, is reduced by half in size and has a low profile structure.
The PIFA is still improved to be multi functional and developed as a dual band antenna used in two different frequency bands. FIG. 2 shows a dual band PIFA antenna 10 using the same operational principle as the PIFA of FIG. 1. The dual band antenna 10 includes a radiating patch 12 a shorting pin 14 coupling the radiating patch 12 to a ground, a coupling feed pin 15 feeding current to the radiating patch 12, a dielectric block 11 having a ground plane (plate). A slot S having a U shape is formed inside the radiating patch 12 to have the dual frequency bands and divides the radiating patch 12 into two radiating patch areas to induce (direct) the current fed through the coupling feed pin 15 along the slot S to have a resonance electric length corresponding to two different frequency bands. The dual band antenna 12 may be used in a dual frequency band, for example a GSM frequency band and a DCS frequency band.
However, recently, the frequency band is variable to a CDMA frequency band (about 824-894 MHz), a GPS frequency band (about 1570-1580 MHz), a PCS frequency band (about 1750-1870 MHz or 1850-1990 MHz), or a blue tooth frequency band (2400-2480 MHz). The PIFA antenna is required to have a multi frequency band rather than the dual frequency band because the above conventional slot of the dual band antenna is not suitable to the multi band antenna. If the dual band antenna is built in the mobile communication terminal, the profile becomes too low, and a frequency bandwidth becomes too narrow.
Since a height of the dual band antenna, which is a major factor in designing the PIFA, is limited due to a limited width of the mobile communication terminal for the portability and a neat appearance, the narrow frequency bandwidth is disadvantageous in the mobile communication terminal.
A distribution circuit, such as a chip type LC component, may be additionally attached to the dual band antenna in order to remove the above problem. Although the dual band antenna obtains a much wider frequency bandwidth by controlling the impedance matching using the distribution circuit, unexpected problems, such as an efficiency of the dual band antenna, occur because the dual band antenna is interfered with the distribution circuit, which is an outside circuit coupled to the dual band antenna.
Therefore, we contemplate a PIFA to have a low profile structure, to be able to be used in a variety of frequency bands, and to improve characteristics of the narrowed frequency bands.
In order to overcome these and other problems, it is an object according to the present invention to provide a planar inverted F antenna having a LC coupled feed line spaced-apart from a radiation patch having a conductive pattern to obtain multi frequency bands each having a much wider frequency band width.
Additional objects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice.
These and other objects may be achieved by providing a planar inverted F antenna (PIFA) having predetermined structure, function, and shape of a feed line according to embodiments of the present invention.
According to an aspect of the present invention, the PIFA includes a feed pin directing a current, a feed line having one end electrically coupled to one end of the feed pin and having a predetermined resonance length, a coupling pin coupled to the other end of the feed line, and a radiating patch formed on a plane spaced-apart from the feed line by a predetermined distance to induce (feed) the current directed (fed) through the other end of the coupling pin, and a slot having one end starting at a portion of an edge and the other end disposed in an inside portion of the radiating patch, and a shorting pin having one end coupled to the radiating patch and the other end coupled to a ground.
According to another aspect of the present invention, the PIFA may include a feed pin directing a current, a feed line having one end electrically coupled to one end of the feed pin and having a predetermined resonance length, a radiating patch being spaced-apart from the feed line and being supplied through the feed pin, a shorting member having one end coupled to the radiating patch and the other end formed with a coupling pad to be coupled to a ground plate of a housing of a telecommunication terminal and to the other end of the feed line.
The PIFA may include a feed pin supplying a current, a first feed line having one end electrically coupled to one end of the feed pin and having a first resonance length, a second feed line having one end coupled to one end of the feed pin to be parallel to the first feed line and having a second resonance length, a radiating patch having a slot starting at an edge of the radiating patch and extended to an inside portion of the radiating patch, the radiating patch divided by the slot into a first patch area supplied with the current through the other end of the feed pin and a second patch area supplied with the current through the other end of the second feed line, a coupling pad formed to couple the radiating patch to a ground of a housing of a telecommunication terminal, and a shorting member having one end coupled to the coupling pad coupled to the other end of the first feed line and the other end coupled to the other end of the first patch area.
The PIFA may be formed with an LC coupling unit capable of adjusting a capacitance of an antenna by an area of the feed line and a distance with the radiating patch and controlling an inductance of the antenna by using a length of the feed line when the feed line having a predetermined resonance length is disposed to be spaced-apart from the radiating patch. The PIFA allow the frequency band to be expanded. A multi band antenna can be easily designed with various structures of the feed lines.
The feed line is coupled to the feed pin at one end thereof. There exist two different types of the feed lines in accordance with a coupling structure of the other end of the feed lines.
A first type feed line has the other end coupled to the radiating patch to be supplied with the current and combined with the radiating patch to have an electrical resonance length. A second type feed line has one end and the other end coupled to a feed pin and the shorting pin (or the coupling pad disposed below the shorting pin) to form the electrical resonance length. The above first type feed line and the second type feed line may be combined to form a third type feed line.
The LC coupled feed line has a predetermined electrical resonance length and one of various types of conductive patterns each disposed on a plane spaced-apart by a distance from another plane on which another conductive pattern (e.g. radiating patch) is formed to obtain different resonance length(s). The feed line may have a simple loop shape, a meander shape, and a combination of the simple loop shape and the meander shape.
A portion of the feed line disposed on a first plane is extended to a second plane different from and spaced-apart from the first plane. When the antenna is formed with at least two dielectric layers, and when the feed line has a first portion having a first conductive pattern and a second portion having a second pattern, the first portion and the second portion of the feed line are formed on the same plane or respective different planes. This antenna has the different electrical resonance lengths as well as the low profile.